Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$246.78	3.533%	$255.4987	$255.50	$255.50	$255.50
Purchase #2	$44.31	5.839%	$46.8973	$46.90	$46.90	$46.90
Purchase #3	$118.41	7.497%	$127.2872	$127.29	$127.30	$127.30
Purchase #4	$43.74	4.507%	$45.7114	$45.71	$45.70	$45.70
Purchase #5	$179.88	5.568%	$189.8957	$189.90	$189.90	$189.90
Purchase #6	$23.29	10.622%	$25.7639	$25.76	$25.75	$25.80
Purchase #7	$125.29	8.240%	$135.6139	$135.61	$135.60	$135.60
7 purchase totals =	$781.70		$826.6681	$826.67	$826.65	$826.70